Voltage Drop

[Hickers]

Hi, not a problem but like to understand why my shore power voltage, in a 240 volt system, drops from an indicated 244 volts to 232 volts when my air conditioning is running. The air draws about 6.7 amps. Thanks.

 

[wwestman]

Takes a while for the power plant to spin up the another generator to carry the extra load. Obviously I have no idea but then it is all just black magic to me.

 

[Insequent]

The normal reason for voltage drop is undersized wiring for the load. You might indeed have a problem! You should not be seeing it on the 240VAC supply. Could be that with aircon running you are sucking too much juice from the supply you are connected to? Perhaps you are hooked up to a 10 A outlet? The thing is, there will be overheating in wiring when voltage drop occurs. That could start a fire. I would try and get it sorted if I could.

 

[DavidM]

Tell us more about how you are hooked up to power: 240V/50A shorepower presumably. How long are your shore power cords?

But I agree, a 12V drop with a 7 amp load is way too much. You can troubleshoot by hooking a voltmeter to the backside of your shore power inlet, perhaps at the breaker near the inlet. Turn on the A/C. If the voltage drops, then the problem is in your cord, the inlet itself or the marina wiring. If no or little voltage drop then the problem is in your boat.

If the voltage drops significantly in the test above, then with the marina's help connect your voltmeter to the backside of their shorepower socket and do the same thing. If the voltage doesn't drop then the problem is in your shorepower cord or its connections. If the voltage drops, then the problem is in the marina supply wiring.

David

 

[High Wire]

Otherthings you can do:
Disconnect each plug and inspect for green or blue corrosion and or heat damage such as melted insulation or conductors turn dark.
After being loaded for a while carefully feel the cord connectors for heat. A bad connection causes high resistance, high resistance with current flow generates heat.
Question: does 6.7 amps include water pump and blower current?
Question: If you turn on the microwave with the air on, how low does the voltage go?

 

[Gordon J]

Probably not a problem

Hi, not a problem but like to understand why my shore power voltage, in a 240 volt system, drops from an indicated 244 volts to 232 volts when my air conditioning is running. The air draws about 6.7 amps. Thanks.

This happens on our Dock every summer. I don't think the problem is so much with your boat as it is with the dock. Your dock can only supply so much juice. The higher the demand, the less is available for everyone. Your electrical equipment is more than likely built to take 10 % more or less voltage than nominally specified.

Gordon

 

[DavidM]

This happens on our Dock every summer. I don't think the problem is so much with your boat as it is with the dock. Your dock can only supply so much juice. The higher the demand, the less is available for everyone. Your electrical equipment is more than likely built to take 10 % more or less voltage than nominally specified.

Gordon

While I agree that dock wiring can be marginal and 5 or even 10% voltage drop is tolerable, I think that his problem is specific to his boat, his shore power wiring or maybe the dock pedestal.


He measured a 12V voltage drop while adding 7 amps. If it were really the marina's general wiring, if 3 neighbors did the same thing, the voltage would drop to below 200.


But until the OP tells us more about where and how he is plugged in, we are all just speculating.


David



David

 

[diver dave]

Hi, not a problem but like to understand why my shore power voltage, in a 240 volt system, drops from an indicated 244 volts to 232 volts when my air conditioning is running. The air draws about 6.7 amps. Thanks.

You are describing (244-232) x 6.7 = 80 Watts of loss in the upstream wiring system. Your load is about 1500 Watts. Some of that loss will be in either side of the shore power cord connections. I would definitely check for heat rise at each end. Some of the loss will be in the wiring itself, the various circuit breakers upstream, and the marina's transformer. But, something is not right here.

 

[TomandJeri]

6-gauge copper is around 0.5 ohms per 1000 ft, so a 50 ft cord set (100 ft total) has around 0.05 ohms of impedance. 6.7A x 0.05 ohms = .34 volts dropped in the cord. There's a bad connection(s) somewhere, or serious damage to that cord.



Any chance you have an isolation transformer that's already overloaded? That's about the only way your 6.7A is going to cause a big voltage sag in a x-former.


I would start in the panel, and retorque connections to busses and breakers. Then work my way out, including the incoming shore power.


Do other circuits suffer the same voltage drop when the A/C is on? If not, it's probably just in the A/C circuit. Where are you measuring the voltage?

 

[rolomart3]

Hi, not a problem but like to understand why my shore power voltage, in a 240 volt system, drops from an indicated 244 volts to 232 volts when my air conditioning is running. The air draws about 6.7 amps. Thanks.

Hi Hicks,


The reason for the drop is that between the power source and the point where you made the reading there is about 1.8 ohms of resistance. The transmission of power is losing 80 watts and operating at a transmission efficiency of about 95%. If the power line goes over a long distance, it is acceptable because over a long distance the dissipated 80 watts of the line would barely raise the temperature of the wire. If the power line is short however, there may be a poor contact involved somewhere and it should be investigated further. A poor contact would be dissipating the 80 watts (very similar amount of heat of a 75 watt incandescent light bulb) at a single point. It can be detected it with a non-contact thermometer.

 

[Hickers]

Thanks for the replies, I might just check my connections!

 

[Xsbank]

Total up all the ac loads on your boat, my money is on overloading. Battery chargers, lights, hot water tank, water pumps, fridge, microwave etc etc. The dock supply is fixed. Measure the voltage at the dock then measure the voltage in a wall plug on your boat and start shutting off loads until it reads the same as the dock. Check your power cords for heat, another indication of overloading.